Thermodynamic properties of the 1D alternating spin (1,1/2) XXZ chain in a finite magnetic field

The Trotter theorem is applied to investigate the mixed-spin (1, 1/2) Heisenberg ferrimagnet chain with exchange anisotropy in a magnetic field. With the help of discretized path-integral representation and the double-chain approximation, the system is mapped onto a double chain in an effective magnetic field. We report the low temperature thermodynamics of the quantum system subject to the field. The quantized magnetization plateau as a function of the field, appearing at a third saturated magnetization, is stable over the whole antiferromagnetic coupling region. The Kosterlitz-Thouless transition point (owing to the anisotropy) is obtained in ferromagnetic coupling region alpha(c) similar or equal to -0.9. The double-peak structure in the specific heat curve is also found, which comes from the huge variation of the long-range order. (C) 2002 Published by Elsevier Science Ltd.